Changes in tissue and cerebral oxygenation following spinal anesthesia in infants: a prospective study
This study is a prospective, non-randomized, non-blinded study looking at the effect of awake spinal anaesthesia on cerebral and regional Near Infra Red Spectroscopy (NIRS) in infants. This study seeks to add further information to the debate about possible toxicity of anaesthesia in infants. It uses a recent article describing a reduction in cerebral blood flow (measured by transcranial doppler) in the setting of awake spinal anaesthesia (SA) as the premise for studying the effect on NIRS of awake SA. 23 infants with a median age of 7 months and median weight of 8kg were studied with recruitment based on convenience and availability of staff to conduct the test. Infants had EMLA cream applied to their lumbar area. Spinal anaesthesia with 1mg/kg hyperbaric 0.5% bupivacaine, 1:200000 adrenaline and 1mcg/kg clonidine was established in the sitting position. One patient was given 3mcg/kg clonidine as an oral premed so did not receive intrathecal clonidine. 2 further patients did not receive intrathecal clonidine for unspecified reasons. 4 patients did not have SA successfully established so were excluded from the study. IV access was established in the lower limb after spinal blockade and an average of 18ml/kg IV fluid was given throughout the case. NIRS was measured at the forehead and the thigh at time points before Spinal Anaesthesia (SA), immediately after SA and then at intervals of 1 minute for a total of 30 minutes. No further sedative or analgesic medications were given, and all patients breathed room air throughout. Temperature was not measured but warming of the room occurred and radiant heaters were employed in an unspecified number of patients. One patient was converted to GA at surgical request after the 30 minutes were up.
- Mean baseline cerebral saturation was 73%. Immediately after SA it was estimated to be 67%, and after 30 minutes to be 68%.
- Mean baseline tissue saturation was 80%. Immediately after SA it was estimated to be 91%, and after 30 minutes to be 93%.
- Mean MAP decreased from 58 to 46mmHg and mean heart rate decreased from 149 to 127 after 30 minutes.
The raw data are not published in the paper itself, rather only in an online supplement. The only data given in the paper are the statistical coefficients calculated by the very complex statistical computations, making the data impenetrable to the average reader. The stated aim of the study was to investigate the effect of awake spinal anaesthesia on cerebral blood flow and in particular cerebral and tissue oximetry. There was no direct measure of cerebral blood flow used in the study. The study appears to show an immediate drop in cerebral NIRS after SA initiation but fails to comment on this, instead choosing to present statistics showing no change in cerebral NIRS during the following 30 minutes. The authors go on to write that although there were decreases in haemodynamic parameters after SA placement, “these did not require treatment”. They do not specify what they mean by “require” or at what point they would intervene. They quote another study looking at cerebral NIRS after SA in which 103 patients were studied (5 times the number studied here) which also showed no decline in cerebral NIRS after spinal anaesthesia. It seems that this study with less than 20 patients included in final analysis does not add anything to the already published paper.
Take Home Message
This study is of poor methodological design with no calculation of the numbers needed to prove or refute a hypothesis that is not clearly stated. It does not answer an important clinical question and is conducted in a patient population (7-month-old 8kg infants) that would seldom be considered for awake spinal anaesthesia in most centres in Australia or New Zealand. It is confounded by the addition of clonidine in the spinal which is known to be systemically absorbed.
Reviewed by: Dr Paul Davies